There is a need for paints for use on vehicles such as automobiles and motorcycles where the paint films have excellent solvent resistance, gasoline resistance and weather resistance without loss of the paint film hardness or appearance. In particular, paints which have a high scratch resistance have recently become important in view of the problem of the scratching of the paint film in automatic car-wash facilities.
Paint compositions which contain from 10 to 50 weight % (wt %) of a urethane polyol obtained by reacting an isocyanate compound and caprolactone polyol and of which the weight average molecular weight is from 1,500 to 4,000 and the hydroxyl group value is from 50 to 180 mgKOH/g, from 30 to 80 wt % of fluorinated resin copolymer in which fluoro-olefin has been reacted as an essential raw material component and of which the hydroxyl group value is from 50 to 150 mgKOH/g and from 10 to 40 wt % crosslinking agent are known as paint compositions where scratch resistance is imparted to the paint film and which provide paint films with which the initial water-repelling properties are maintained (for example, Japanese Unexamined Patent Application Laid Open H5-051556). However, these paint compositions have a weakness in that the wettability of a water-based base-coat is reduced by the water-repelling properties of the fluorinated resin copolymer.
Furthermore, paint compositions which are characterized by containing as a hardenable resin composition (A) from 90 to 50 wt % of acrylic copolymer of hydroxyl group value from 60 to 140 mgKOH/g and weight average molecular weight from 3,000 to 30,000 constructed with styrene monomer, monomer which includes 1,4-butanediol mono-acrylate monomer and/or ε-caprolactone modified acrylate monomer as hydroxy group-containing mono-acrylate monomer, and acrylic acid ester monomer of primary alcohol which has from 4 to 24 carbon atoms and of which said styrene monomer content is from 45 to 55 wt %, and (B) from 10 to 50 wt % amino resin and/or (blocked) polyisocyanate compound are known as top-coat paints for automobile painting purposes which have excellent acid resistance, weather resistance and scratch resistance (for example, Japanese Unexamined Patent Application Laid Open H5-320562). However, these paint compositions have a weakness in that the dirt-soiling resistance is reduced since the glass transition point (Tg) of the paint film is low because an amount of 1,4-butanediol mono-acrylate monomer with which the scratch resistance is satisfactory is used.
Furthermore, an ultraviolet-hardening type paint composition which contains (A) ultraviolet hardenable polyfunctional (meth)acrylate of functionality at least 4 of number average molecular weight from 300 to 2,000 which has in one molecule at least four (meth)acryloyl groups, (B) lactone modified polyhydric alcohol mono(meth)acrylate polymer which contains from 20 to 60 wt % ring-opened ε-caprolactone adduct and of which the hydroxyl group value originating from the lactone modification is from 100 to 180 mgKOH/g and (C) non-yellowing type polyisocyanate compound in which in respect of the total amount of the (A), (B) and (C) components there is from 10 to 50 wt % of the (A) component and from 90 to 50 wt % of the (B) and (C) components and in which there are from 0.5 to 1.5 equivalents of (C) component isocyanate group per 1 hydroxyl group equivalent of the (B) component, and which also contains (D) photo-stabilizer and (E) photo-polymerization initiator which is characterized in that the Knoop hardness of the hardened paint film obtained from said ultraviolet-hardening type paint composition is from 10 to 18 and the molecular weight between crosslinks of the hardened paint film is from 150 to 300, is known as an ultraviolet-hardenable paint which has excellent scratch resistance, which has a beautiful appearance and which has good adhesion properties and gasoline resistance (for example, Japanese Unexamined Patent Application Laid Open 2003-277684).
However, these paint compositions have a weakness in that ultraviolet radiation must be used for the hardening reaction.
Furthermore, (A) pre-polymers which have difunctional and/or trifunctional terminal NCO groups which have been obtained by reacting an aliphatic diisocyanate or alicyclic diisocyanate with a polycaprolactone diol and/or triol of number average molecular weight from 500 to 1,500 and then essentially removing the unreacted aliphatic diisocyanate or alicyclic and diisocyanate and (B) acrylic polyols of glass transition point from 30 to 100° C. which have a hydroxyl group value of from 10 to 150 mgKOH/g based on the resin, in an NCO/OH equivalent ratio of from 0.5 to 2.0 are known to form two-liquid type polyurethane paint films which provide excellent scratch resistance to acrylic moldings. (For example, Japanese Unexamined Patent Application Laid Open H11-042746) However, these paint compositions have a weakness in that the paint film retains a tacky feel because a film which is extensible is formed.